Here's the problem: I have three cameras, a Panasonic GH2 and two GH1s. I will be shooting weddings with them.

The GH2 will be shooting in 1080i, because I cannot use my monitor in any other mode with the camera, and because it is my primary cam, I must use a monitor.

The GH1s will be shooting in 720p, because it doesn't shoot in 1080i, well it does, but its 24fps mode, which I don't think I want to use.

So the end result will be I will end up with 1080i and 720p footage, and most of it will end up on an SD DVD. On occasion it will end up on Blu ray, but only occasionally. I suppose I just use a program to resize all of it to avi, edit the avi, then render out to DVD.

Will tmpgenc work for this process? When I need a bluray disc, then what do I do? Anyone have any experience with a similar scenario?

What I would do is edit the mixed footage on a 720p timeline. This means for the 1080 footage you will need to either "fit to frame" or resize manually, pan n' scan if you like, etc., but however you do it, get the entire project to 720 format
In my experience the 720 HD edit will produce a higher quality DVD image than you would get from rescaling the entire shoot to SD.avi, editing, then transcoding to DVD.
For BR, there is a 720 spec, so you do have the option to take the HD timeline out to BR.
The alternative of rescaling the 720 up to 1080 is not as good. You will lose image quality when you enlarge the 720, and even though you end up downscaling to DVD, the quality hit will still be noticable- it will be "baked in" in the edit.

Thanks for your input Robert, not bad advice. I have had this conversation before, and have forgotten what was recommended. In the previous case though I wasn't mixing footage.

I think what I might do initially is to convert the 1080i to 720p. Vegas doesn't resize avchd very well.

I haven't tried this yet, so what I'm saying here is theoretical and not from experience.

When you downconvert 1080i into 720p, you may be getting some bizarre artifacts due to that interlacing inside 1080. A progressive image can down- (or up-)convert fairly well, but changing image size when the timeline is interlaced requires a lot of intelligent processing of that interlaced video in order to avoid some weird jagged lines in fast-moving scenes.

Carefully test this workflow before committing. In the end, you may even get better results from up-converting 720p to 1080i and editing all of it on a 1080i timeline.

Predrag, since I will have two cameras with 720p, it would seem good to convert the 1080, since it's only 1 camera.

It would certainly be a more efficient path (down-converting one set of files, rather than up-converting two sets). The question is whether that down-converted 1080i would actually look acceptable if not properly de-interlaced and downsampled to 720p.

If it were not properly deinterlaced it would look terrible, of course.